diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 9db90c872..3d8b2a0c4 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -198,6 +198,9 @@ void RemoteStore::setOptions()
         writeInt(logType, to);
         writeInt(printBuildTrace, to);
     }
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 6) {
+        writeInt(buildCores, to);
+    }
     processStderr();
 }
 
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index e44c1e36b..5504773b8 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -8,7 +8,7 @@ namespace nix {
 #define WORKER_MAGIC_1 0x6e697863
 #define WORKER_MAGIC_2 0x6478696f
 
-#define PROTOCOL_VERSION 0x105
+#define PROTOCOL_VERSION 0x106
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
diff --git a/src/nix-worker/nix-worker.cc b/src/nix-worker/nix-worker.cc
index 0052fbb7d..13cecf654 100644
--- a/src/nix-worker/nix-worker.cc
+++ b/src/nix-worker/nix-worker.cc
@@ -500,6 +500,9 @@ static void performOp(unsigned int clientVersion,
             logType = (LogType) readInt(from);
             printBuildTrace = readInt(from) != 0;
         }
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 6) {
+            buildCores = readInt(from);
+        }
         startWork();
         stopWork();
         break;